I think this episode shows an interesting and subtle commentary on attitudes to homosexuality, and also uses the Trill symbiosis concept to good effect.
The thing is, I think the episode does a rather clever thing by reminding us that what comes naturally in sexuality isn't as straightforward as some people like to think. For the Joined Trill, the symbiont and its bank of past lives are part of the host (and vice versa), and their acting on and influencing the current host is an outgrowth of how a Joined Trill naturally works. And we see from Jadzia's friendship with Curzon's friend Sisko, and later Ezri's friendship with Jadzia's friends, that in most circumstances the past lives aren't suppressed or denied but integrated healthily into the current life. So past life informing present is natural for Joined Trills. As I'm sure we're all aware, one of the more common lines from those who are anti-homosexuality is the idea that homosexual acts "aren't natural", which seems to assume that the purpose of sexuality is straight-forward reproduction, and that any sex not geared towards that end is without purpose and so without justification. That of course overlooks the fact that intelligent species are drawn to have sex for a variety of different purposes - dolphins have sex for pleasure, bonobos have sex to reaffirm social ties and forge close relationships. Humans (a particularly social and intelligent species) do both; they have sex to affirm or forge close bonds of affection, and to enjoy themselves, among other reasons. So there's a lot more to "natural" than simple reproduction - and some humans have their sexuality focused on non-reproductive partners.
It seems to me that this epsiode cleverly reproduces this model in an interesting way. We know Jadzia is apparently heterosexual, so when we see her going after a woman we think "that's not normal" (meaning, not normal for her). But then we remember the key point: she's also
a Joined Trill, and it seems that it is
natural and normal for the symbiont part of the joined consciousness to seek out old partners (despite Trill society’s efforts to suppress it). Or, in other words, the question of what's a "natural" and normal aspect of Jadzia's sexuality is a more complicated subject than might first appear. Is it normal for a baseline-heterosexual Trill to be drawn sexually to another member of their sex? Well, if they’re both Joined, then yes. We're reminded that there's more going on in Jadzia Dax's sexuality than her host's heterosexual nature, if that makes sense. Taking it as an analogy for more general sexuality, we're reminded that in wider human nature there's more to the subject than simple reproduction. Jadzia's Joined Trill sexuality isn't one-note, and nor is real sexuality. Is it normal for a human to sexually desire members of the same sex? If they're a certain type of person, then yes.
On a note only loosely related, this episode does have (sadly) a bad case of "As You Know Bob" at the beginning, regarding how Trills work. Excusable, perhaps, because of how important it is that the audience understands the Trill set up - and naturally that reinforces the point that the symbiosis angle is integral to the episode.